An electrolytic capacitor typically has such a structure shown in FIG. 1. That is, an anode electrode foil 2 is made of a band-shaped high purity aluminum foil where the effective aluminum foil surface has been enlarged through etching process chemically or electrochemically, and an oxide film is formed on the surface, through a chemical process of treating the aluminum foil with a chemical solution such as ammonium borate aqueous solution and the like. A cathode electrode foil 3 is also made of an etched aluminum foil of high purity. Capacitor element 1 is formed by the anode electrode foil 2 and the cathode electrode foil 3, wound together with intervening separator 11 made of manila paper and the like. Next, the capacitor element 1, after impregnating with electrolyte solution for driving the electrolytic capacitors, is housed into a bottomed outer case 10 made of aluminum and the like. The outer case 10 is equipped at the opening with a sealing member 9 made of an elastic rubber, and is sealed by drawing.
The anode electrode foil 2 and the cathode electrode foil 3 are each connected to lead wires 4 and 5, employed as electrode leading means to lead the electrodes, by means of stitching, ultrasonic welding, and the like, as shown in FIG. 2. Each of the lead wires 4 and 5 employed as electrode leading means is comprised of a rod member 6 made of aluminum, a connecting member 7 that comes into contact with each of the electrode foils 2 and 3, and an outside connecting member 8 made of solderable metal which has been fixed at the tip of the rod member 6.
Herewith, as electrolyte solution for driving the electrolytic capacitor having high conductivity, and to be impregnated to the capacitor element, wherein γ-butyrolactone is employed as the main solvent composed of quaternized cyclic amidin compounds (imidazolinium cation and imidazolium cation) as the cationic component and acid conjugated bases as the anionic component are dissolved therein as the solute (refer to Unexamined Published Japanese Patent Application No. H08-321449 and No. H08-321441)
However, due to the remarkable development of digital information devices in recent years, the high-speed driving frequency of micro-processor which is a heart of these electronic information devices is in progress. Accompanied by the increase in the power consumption of electronic components in the peripheral circuits, the ripple current is increased abnormally, and there is a strong demand for the electrolytic capacitors used in these circuits to have a low impedance characteristic.
Moreover, in the field of vehicles, with the recent tendency toward improved automobile functions, a low impedance characteristic is in high demand. By the way, the driving voltage of the vehicle circuit of 14V has been progressed to 42V accompanied by the increase in the power consumption. To comply with such a driving voltage, the electrolytic capacitor requires the withstand voltage characteristic of 28V and 84V and more. Furthermore, the electrolytic capacitors must withstand high temperature in this field, and a high temperature life characteristic is in demand.
However, the electrolytic capacitor cannot cope with the low impedance characteristic as such, Moreover, although the withstand voltage of 28V is capable, the limit is 30V, and it cannot respond to the requirement of the high withstand voltage of 84V and more. Moreover, these electrolytic capacitors suffer from a problem that the electrolyte solution would leak between the sealing member 12 and the perforation hole of the lead wire 5 for leading the cathode electrode. The electrolyte solution leakage invites the deterioration electronically such as decline in electrostatic capacity of the electrolytic capacitor resulting in the disadvantage of the short life of the electrolytic capacitors.
The problem with a small-sized electrolytic capacitor has been described so far. A similar problem does exist with a large-sized electrolytic capacitor. That is to say, in regard to the electrolytic capacitor shown in FIG. 3, it had a problem of leakage occurring from a contact portion with the rivet 15 and the sealing component 13 of the cathode electrode side.
Henceforth, the present invention aims to provide an electrolytic capacitor, having a low impedance characteristic and a high withstand voltage characteristic of 100V class, and excellent in high temperature life characteristic and leakage characteristic.